The present invention relates to a liquid crystal display device, more particularly to a liquid crystal display device adopting a driving method in which scanning signals are applied to two gate buslines simultaneously.
In resent years, development of active-matrix liquid crystal display devices using thin-film transistors as switching elements for driving liquid crystals has been actively carried out. The following description will explain a liquid crystal display device integrated with a driver, as an example of the active-matrix liquid crystal display device.
FIG. 8 is a plan depiction of the liquid crystal display device integrated with a driver. In the liquid crystal display device integrated with a driver, as illustrated in FIG. 8, a gate driver 32, a source driver 33, and a thin film transistor (hereinafter referred to as xe2x80x9cTFTxe2x80x9d) array section 34 are disposed on a substrate 31 made of glass or quartz.
The gate driver 32 includes a shift register 32a and a buffer 32b. The source driver 33 includes a shift register 33a, a buffer 33b, and analog switches 39 for sampling video lines 38.
In the TFT array section 34, a number of gate buslines 116 running from the gate driver 32 are arranged parallel to each other. A number of source buslines 120 running from the source driver 33 are arranged to cross the gate buslines 116 at right angles. Moreover, additional capacitance common lines 114 are arranged parallel to the gate buslines 116.
A TFT 35, a pixel 36, and an additional capacitor 37 are provided in each rectangular region enclosed by one gate busline 116, two adjacent source buslines 120, and one additional capacitance common line 114. The gate electrode of the TFT 35 is connected to the gate busline 116, while the source electrode thereof is connected to the source busline 120. A liquid crystal is sealed in a space between a pixel electrode connected to the drain electrode of the TFT 35 and a counter electrode, thereby forming a pixel 36. The additional capacitance common line 114 is connected to an electrode to which the counter electrode is connected.
As a scanning method used in such a liquid crystal display device integrated with a driver, the following methods are given. One example is a simple scanning method in which a selection signal is separately applied to each gate busline. Another example is a simultaneous two-line scanning method in which two gate buslines are simultaneously driven. Here, the simultaneous two-line scanning method will be explained with reference to FIG. 9.
According to the simultaneous two-line scanning method, in an odd-numbered field, first, scanning signals are simultaneously applied to the first and second gate buslines G1 and G2. Then, after a delay of one horizontal scanning period, scanning signals are simultaneously applied to the third and fourth gate buslines G3 and G4. Thus, scanning signals are simultaneously applied to an odd-numbered gate busline and the next (i.e., even-numbered) gate busline, and then to the subsequent odd-numbered gate buslines and even-numbered gate buslines in this manner successively.
On the other hand, in an even-numbered field, first, a scanning signal is applied to the first gate busline G1. Then, after a delay of one horizontal scanning period, scanning signals are simultaneously applied to the second and third gate buslines G2 and G4. Furthermore, scanning signals are simultaneously applied to the fourth and fifth gate buslines G4 and G5. Hence, in an even-numbered field, scanning signals are simultaneously applied to a combination of adjacent gate buslines which is different from a combination of adjacent gate buslines in an odd-numbered field.
Accordingly, the simultaneous two-line scanning method requires twice the gate buslines and pixels electrodes compared to the simple scanning method in which a scanning signal is separately applied to each gate busline. However, the simultaneous two-line scanning method provides images of high resolution according to an interlace method.
In this case, since there is a need to perform a.c. driving of the liquid crystal display device, positive and negative video signals are alternately applied to a single pixel electrode every other field, i.e., a positive video signal is applied to a pixel electrode in one field and a negative video signal is applied to the pixel electrode in the next field. However, when the polarities of the video signals to be applied to pixel electrodes forming one screen are inverted every field, the flicker increases. In order to solve such a problem, for example, Japanese publication of examined patent application (Tokukohei) No. 7-113819/1985 proposes a method of inverting the phases of the video signals every two gate buslines which are to be scanned simultaneously.
In the first field, as shown in FIG. 10(a), positive video signals (indicated by xe2x80x9c+xe2x80x9d) are applied to the pixel electrodes connected to the first and second gate buslines G1 and G2 which are selected simultaneously. Meanwhile, negative video signals (indicated by xe2x80x9cxe2x88x92xe2x80x9d) are applied to the pixel electrodes connected to the third and fourth gate buslines G3 and G4 which are selected simultaneously. Moreover, the positive video signals are applied to the pixel electrodes connected to the fifth and sixth gate buslines G5 and G6 which are selected simultaneously.
In the second field, as illustrated in FIG. 10(b), a positive video signal is applied to the pixel electrode connected to the first gate busline, negative video signals are applied to the pixel electrodes connected to the second and third gate buslines G2 and G3 which are selected simultaneously, and positive video signals are applied to the pixel electrodes connected to the fourth and fifth gate buslines G4 and G5 which are selected simultaneously.
In the third field, as shown in FIG. 10(c), video signals whose polarities are opposite to those applied in the first field are applied to the pixel electrodes connected to the respective gate buslines. In the fourth field, as shown in FIG. 10(d), video signals whose polarities are opposite to those applied in the second field are applied to the pixel electrodes connected to the respective gate buslines.
In the above-mentioned method, it is possible to reduce the flicker as compared to a method in which the polarities of the video signals to be applied to the pixel electrodes of one screen are inverted between positive (+) and negative (xe2x88x92) every field. However, according the above-mentioned method, the polarity of the pixel electrode connected to the first gate busline G1 changes every field in order of +, +, xe2x88x92,xe2x88x92. The polarity of the pixel electrode connected to the second gate busline G2 changes every field in order of +, xe2x88x92, xe2x88x92, +. The polarity of the pixel electrode connected to the third gate busline G3 changes every field in order of xe2x88x92, xe2x88x92, +, +. The polarity of the pixel electrode connected to the fourth gate busline G4 changes every field in order of xe2x88x92, +, +, xe2x88x92. Thus, since the cycle of inverting the polarities of the video signals applied to the respective pixel electrodes is four fields, flicker is generated. As a result, the liquid crystal display device exhibits unpleasant displays.
It is an object of the present invention to provide a liquid crystal display device capable of reducing flicker even when scanning signals are simultaneously applied to two gate buslines by a gate driver.
In order to achieve the above object, a liquid crystal display device of the present invention includes:
a first substrate having gate buslines, source buslines, switching elements which are arranged in the vicinity of intersections of the gate buslines and source buslines so as to form a matrix pattern, and a pixel electrode array formed by pixel electrodes connected to the switching elements;
a gate driver and a source driver, for driving the switching elements;
a second substrate having a counter electrode formed thereon; and
a liquid crystal material sandwiched between the first and second substrates,
wherein the gate driver applies scanning signals simultaneously to two gate buslines located adjacent to each other, and
the source driver applies video signals of opposite polarities to adjacent source buslines, respectively, and inverts the polarities of the video signals every vertical scanning period.
According to this structure, the gate driver performs simultaneous two-line scanning by applying scanning signals simultaneously to two gate buslines located adjacent to each other, and the source driver applies video signals of opposite polarities to adjacent source buslines, respectively. Since the polarities of the video signals are inverted every vertical scanning period, the cycle of inverting the polarities of the video signals to be applied to the pixel electrodes is as short as two fields. Moreover, since the polarities of the video signals are inverted every source busline, the liquid crystal display device of the present invention can reduce flicker generated in the liquid crystal display device.
Moreover, the liquid crystal display device of the present invention is preferably arranged so that a plurality of video signal lines for feeding the video signals are provided, and the polarities of the video signals to be input to the video signal lines are inverted every vertical scanning period.
With this structure, since a plurality of video signal lines for feeding the video signals are provided, the polarities of the video signals to be input to the video signal lines can be inverted every vertical scanning period. Thus, in the liquid crystal display device of the present invention, there is no need to perform inversion of the polarities of the video signals every source busline which is required in a liquid crystal display device having a single video signal line.
Furthermore, the liquid crystal display device of the present invention is preferably arranged so that the polarities of the video signals to be applied to the pixel electrodes of adjacent columns of the pixel array are opposite to each other.
With this structure, since the polarities of the video signals to be applied to the pixel electrodes located adjacent to each other in a column direction of the pixel array are respectively inverted, the liquid crystal display device of the present invention can further reduce flicker as compared to a liquid crystal display device in which the polarities of the video signals are only inverted every source busline.
In addition, the liquid crystal display device of the present invention is preferably arranged so that the switching elements connected to the source buslines are positioned alternately on one side and the other side of the source buslines.
With this structure, since the positions of the switching elements with respect to the source buslines change alternately between the right side and left side of the source buslines every row, the connecting position of the switching elements to the pixel electrodes changes. Thus, this liquid crystal display device can easily invert the polarity in each pixel.
Besides, the liquid crystal display device of the present invention is preferably arranged so that the gate driver is formed on the first substrate.
With this structure, since the gate driver is formed on the substrate on which the switching elements are formed, it is not necessary to use a complicated external driver IC for scanning two gate buslines simultaneously. Hence, in this liquid crystal display device, it is possible to fabricate the gate driver in the process of forming the switching elements.
Additionally, the liquid crystal display device of the present invention is preferably arranged so that the gate driver includes a multiplexer which contributes to generation of scanning signals which scan gate buslines sequentially two gate buslines at a time.
With this structure, since the gate driver includes the multiplexer, the liquid crystal display device can reduce the number of external input terminals.
Moreover, the liquid crystal display device of the present invention is preferably arranged so that the gate driver includes, between a shift register and the multiplexer, a logical gate circuit for reducing the number of signals input to the multiplexer to a half.
With this structure, since the gate driver includes a logical gate circuit which reduces the number of output signals from the shift register to a half, the number of control signals input to the multiplexer is reduced.
Furthermore, the liquid crystal display device of the present invention is preferably arranged so that the multiplexer has four control terminals.
With this structure, since the number of control terminals of the multiplexer is four, the liquid crystal display device can simultaneously scan two gate buslines with the minimum number of control terminals of the multiplexer.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.